The present invention relates to needle-bearing medical devices having a retractable needle for injecting fluid into a patient. More specifically, the present invention relates to such a device configured for injecting fluid from a pre-filled cartridge. Preferably, the needle is selectively retractable and re-extendable during use to allow the contaminated needle to be shielded between successive needle injections. In one embodiment of the invention, the needle is permanently retractable after use so that the contaminated needle is shielded to prevent inadvertent contact with the sharpened tip of the needle.
Various types of medical devices employ a needle for piercing the skin of a patient for diagnostic or therapeutic purposes. One such device is a device for introducing medicine from a pre-filled cartridge into a patient. Handling of such medical devices after the needle is withdrawn from the patient can result in transmission of various pathogens, most notably human immunodeficiency virus (HIV), due to an inadvertent needle stick to medical personnel.
Several devices are known that allow fluid to be injected into a patient from a pre-filled cartridge. For instance, in dental practice, a cartridge injector is used for injecting novocaine into a patient. These cartridge injectors are normally made with metal, that may be chrome or nickel plated and are intended to be sterilized by an autoclave after use.
When using a dental injector, it is common to administer several small doses of novocaine. After the first injection, the needle is considered contaminated, and current practice, as outlined by OSHA guidelines, requires recapping the needle. Although recapping by hand is prohibited by OSHA guidelines, some dentists still practice this unsafe technique, which can lead to an inadvertent needle stick. One recommended technique for safely recapping the needle uses a cap holder, mounted to the dental tray being used. Although safer than recapping the needle by hand, using a cap holder still exposes the contaminated needle when the device is moved from the patient""s mouth to the cap holder for recapping. Another problem with recapping is that if the dentist is not careful when centering the needle into the cap, the needle tip can scrape the sidewall of the cap. If this happens, the needle can be dulled or can scrape off small pieces of plastic that could be injected into the patient during subsequent injections.
In light of the foregoing, a medical device is provided that allows a series of injections to be made to a patient. Between each injection, the contaminated needle is shielded against inadvertent contact. After use, the needle is shielded to prevent inadvertent contact with the contaminated needle during subsequent handling of the used device. More specifically, the present invention provides a medical device having a hollow housing for receiving a pre-filled cartridge and a plunger for expelling fluid from the cartridge. A needle having a sharpened tip projects forwardly from the forward end of the housing. A biasing element, such as a spring, is operable to displace the needle rearwardly. A first lock releasably locks the needle in a projecting position in which the sharpened tip of the needle is exposed for use. A second lock releasably retains the needle in a shielded position in which the sharpened tip of the needle is shielded against inadvertent contact. In one embodiment of the invention, a third lock fixedly retains the needle in a second shielded position in which the sharpened tip of the needle is shielded against inadvertent contact, and the needle is substantially permanently retained against further axial displacement.
The present invention also provides methods for safely providing a plurality of injections to a patient from a medical device having a needle with a sharpened tip operable between a projecting position, in which the needle is exposed for use, and a retracted position, in which the needle is shielded against inadvertent contact. According to the method, the patient is pierced with the sharpened tip of the needle, and fluid contained in a cartridge is injected into the patient. The needle is then retracted to a first retracted position so that the sharpened needle tip is shielded against inadvertent contact. The needle is releasably locked in the first retracted position by a first lock. The needle is then re-extended into the projecting position, the patient is pierced a second time, and fluid is injected into the patient a second time. In one method, the cartridge can be removed and a new cartridge inserted to provide additional medication for further injections. In another method, the needle can be permanently locked into a second retracted position so that the sharpened needle tip is shielded against inadvertent contact.